The present invention also relates to a method for operating the hot-forming and press hardening tool for producing formed sheet metal parts with at least partially high-strength properties, wherein during the closing motion and/or at the bottom dead center of the hot-forming tool moving the at least one die segment transverse to the press stroke direction, so that in the die cavity, a section of the die cavity is oriented at plus/minus 20, preferably plus/minus 10° to the press stroke direction and has a contact surface with a formed sheet metal blank that corresponds to at least 80% of the surface pressure of the essentially horizontally oriented sections of the die cavity.
In order to manufacture assembly components, in particular motor vehicle assembly components, it is known to process sheet metal blanks by means of forming processes, in particular press forming in a tool. Formed sheet metal assembly components are produced in this manner for car body fabrication, structural assembly components, but also exterior sheet metal skin assembly components. In these cases, formed sheet metal assembly components are preferably made from steel materials, but also from light-weight metal materials.
In recent years, in particular hot-forming and press hardening technologies have been established, based on which temperable steel alloys can be processed. Based on a pre-heating step, in particular above AC3 temperature, the forming degrees of freedom of a sheet metal blank can increased, allowing highly complex, three-dimensionally shaped assembly components to be produced. The assembly component then remains in the tool and is hardened in a rapid cooling step that involves at least partial martensite formation, so that an assembly component is produced with at least partial high-strength, in particular maximum strength material properties. This results in the production of assembly components that are lighter, while also being harder compared to assembly components that were made in a cold forming step from a conventional steel alloy.
For this purpose, however, it is in particular necessary when using a press forming tool that the die cavity created at the bottom is dead center—and thus when the press forming tool has been fully closed—has a sufficiently large surface contact to the formed sheet metal blank in order to facilitate a good thermal transfer from the still hot, formed sheet metal blank to the forming tool during the cooling process to be performed for quench hardening purposes. The heat is then, for instance, removed by a cooling medium that flows through cooling channels of the forming tool.
This is reflected in the manufacturing and design of a hot-forming and press hardening tool, so that a largest possible surface contact is ensured. However, when operated, the hot-forming and press hardening tool exhibits thermal expansion and shrinkage of the tools themselves. In addition, the blanks made available for processing exhibit production variations, so that only a few tenth of a millimeter can in this case have the effect that, for instance, no longer sufficient surface contact is achieved. Moreover, the forming surfaces are subject to mechanical wear during operation to produce several thousand parts, said wear also having the potential of creating a non-surface contact.
In this regard, a forming tool is, for example, known from DE 10 2013 011 419 A1, wherein a forming tool is split into two parts and is actuated by a second press force applied transverse to the press direction by means of an actuating medium. However, a disadvantage is the significantly more elaborate construction and increased effort to operate such a hot-forming and press hardening tool.